Adrian, Are we talking about the same thing? While what you say is correct we are just talking about matching regex. Regardless of the scenario, _100_ matches 100 anywhere in the path, while ^100$ matches when the path has only 100. Whether or not the route is allowed because of loop prevention is another issue.
On Tue, Oct 20, 2009 at 3:27 PM, Adrian Brayton <[email protected]> wrote: > That is not necessarily correct... Sorry about the long winded explanation! > Lets say you have 3 routers. > > A--------B-------C > > Router A (AS 100) is advertising 10.1.0.0/24 and 10.1.1.0/24 > > Router B (AS 200) - aggregate add 10.1.0.0/22 summary-only as-set > > Router C (AS300) is advertising 10.1.2.0/24 and 10.1.3.0/24 > > Now when Router B advertises that summary, its going to have that summary > route and it will look something like this in a "show ip bgp": Path > {100,300} > > Now, when it goes to advertise it to its eBGP neighbors... No one will > install that route because both routers (A & C) see there AS in the path > info. > > Now, if you were to do this on Router B (Remember, there are 2 AS > paths, {100,300} ) > > ip as-path access-list 1 permit ^300$ > > Route-Map BLAH BLAH BLAH > > aggregate-address BLAH BLAH > > Router A will now have the routes in there because ^300$ was the only thing > permitted when there were "2" as-paths! > > I hope you could follow along with what I wrote... > > ^ Start of string > > $ End of string > > [] Range of characters > > Used to specify range ( i.e. [09] ) > > ( ) Logical grouping > > . Any single character > > * Zero or more instances > > + One or more instance > > ? Zero or one instance > > _ Comma, open or close brace, open or close > parentheses, start or end of string, or space > > > > Expression Meaning > > .* Anything > > ^$ Locally originated routes > > ^100_ Learned from AS 100 > > _100$ Originated in AS 100 > > _100_ Any instance of AS 100 > > ^[09]+$ Directly connected ASes > > > > > On Oct 20, 2009, at 4:09 PM, Joe Astorino wrote: > > Also just to add to what Bryan already said the second example says "it has > to start with 100 and then immediately end"...therefore it would have to > have been originated from AS 100. Additionally, like Bryan said it also > means AS 100 is the only AS in the AS_PATH > > On Tue, Oct 20, 2009 at 3:15 PM, Syed Zaidi <[email protected]> wrote: > >> Whats the difference between.. *_100_ *and *^100$* , to me both seems >> one and the same, however i'm still confused. >> Regards, >> Syed >> >> _______________________________________________ >> For more information regarding industry leading CCIE Lab training, please >> visit www.ipexpert.com >> >> > > > -- > Regards, > > Joe Astorino - CCIE #24347 R&S > Technical Instructor - IPexpert, Inc. > Cell: +1.586.212.6107 > Fax: +1.810.454.0130 > Mailto: [email protected] > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, please > visit www.ipexpert.com > > -- Bryan Bartik CCIE #23707 (R&S), CCNP Sr. Support Engineer - IPexpert, Inc. URL: http://www.IPexpert.com
_______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com
